Java Hibernate Cheat Sheet

Details Hibernate entity mapping annotations, session CRUD operations, HQL and Criteria queries, fetch types, and entity lifecycle states.

3 PagesIntermediateApr 8, 2026

Entity Mapping

Map a Java class to a database table with JPA/Hibernate annotations.

java

@Entity@Table(name = "employees")public class Employee {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Long id;    @Column(name = "full_name", nullable = false, length = 100)    private String name;    @ManyToOne(fetch = FetchType.LAZY)    @JoinColumn(name = "department_id")    private Department department;    @OneToMany(mappedBy = "employee", cascade = CascadeType.ALL, orphanRemoval = true)    private List<Address> addresses = new ArrayList<>();    // getters/setters}

Session & CRUD Operations

Basic Hibernate Session lifecycle and persistence operations.

java

SessionFactory sessionFactory = new Configuration()        .configure("hibernate.cfg.xml")        .buildSessionFactory();try (Session session = sessionFactory.openSession()) {    Transaction tx = session.beginTransaction();    Employee emp = new Employee();    emp.setName("Ada Lovelace");    session.persist(emp);          // INSERT    Employee found = session.get(Employee.class, 1L);  // SELECT by id    found.setName("Ada L.");       // dirty checking auto-updates on flush    session.remove(found);         // DELETE    tx.commit();}

HQL & Criteria API

Query entities with HQL and the type-safe Criteria API.

java

// HQL (object-oriented, entity/field names, not table/column names)List<Employee> results = session.createQuery(        "FROM Employee e WHERE e.department.name = :dept", Employee.class)        .setParameter("dept", "Engineering")        .list();// Criteria API (type-safe, JPA standard)CriteriaBuilder cb = session.getCriteriaBuilder();CriteriaQuery<Employee> cq = cb.createQuery(Employee.class);Root<Employee> root = cq.from(Employee.class);cq.select(root).where(cb.equal(root.get("name"), "Ada L."));List<Employee> list = session.createQuery(cq).getResultList();

Fetch Types & Cascade Options

Control how associated entities are loaded and propagated.

FetchType.LAZY- Load the association only when accessed; default for @OneToMany/@ManyToMany.
FetchType.EAGER- Load the association immediately with the parent; default for @ManyToOne/@OneToOne.
CascadeType.PERSIST- Saving the parent also saves associated child entities.
CascadeType.REMOVE- Deleting the parent also deletes associated children.
CascadeType.ALL- Applies PERSIST, MERGE, REMOVE, REFRESH, and DETACH to associations.
orphanRemoval- Automatically deletes child entities removed from the parent's collection.

Entity Lifecycle States

The states an entity moves through in the persistence context.

Transient- New object not associated with a Session and not saved in the DB.
Persistent (Managed)- Associated with an active Session; changes are tracked and auto-flushed.
Detached- Was persistent but the Session closed; changes are no longer tracked.
Removed- Scheduled for deletion in the current transaction.
Flush- Synchronizes in-memory persistence-context changes to the database, automatically before commit/queries or manually via session.flush().
Merge (Reattachment)- session.merge(detachedEntity) copies a detached entity's state onto a managed instance, reattaching it to the persistence context.

Pro Tip

Watch out for the N+1 select problem with lazy associations accessed in a loop - fix it with a JOIN FETCH in HQL/JPQL or @EntityGraph rather than switching everything to EAGER.

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